JPH057548Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a low frequency excitation type electromagnetic flowmeter.

In general, an electromagnetic flowmeter applies a magnetic field to the fluid flowing through a pipe at right angles to the flow direction, and at the same time detects changes in electrical signals in the fluid flow path using a pair of electrodes installed in the pipe. The device is configured to measure the flow rate of the fluid. Many modern electromagnetic flowmeters use low-frequency excitation methods, such as trapezoidal wave excitation and square wave excitation, which have superior zero point stability compared to AC excitation and DC excitation methods. There is. In this type of low-frequency excitation type electromagnetic flowmeter, the current supplied to the excitation coil is periodically switched between two steady-state values, and the induced voltage generated between the electrodes is sampled when the excitation current becomes constant. By taking the difference between adjacent sampling signals, the influence of electrochemical DC voltage and circuit-based offset voltage is removed, and a signal corresponding to the fluid flow rate is obtained. Even in such a constant frequency excitation type electromagnetic flowmeter, if the degree of fluid filling in the pipe line falls below the allowable value and becomes a non-full state,
The measured value of the electromagnetic flowmeter becomes unstable and does not indicate the actual flow rate. Therefore, it is desired to detect the non-full state of the fluid in the pipe.

In the present invention, in addition to a signal component corresponding to the flow rate of the fluid, the voltage generated at the electrode has a different waveform when the water is full and when the water is not full, and includes a noise component that is sufficiently larger than the signal component. By focusing on the fact that the water is not full of water and detecting the noise component when the water is not full, we have realized a low-frequency excitation type electromagnetic flowmeter that can effectively detect the non-full water state.

FIG. 1 is a connection diagram showing one embodiment of the electromagnetic flowmeter of the present invention. In the figure, reference numeral 1 denotes an electromagnetic flowmeter transmitter, which includes an exciting coil L, a pipe P through which fluid flows, and a pair of electrodes G ₁ and G ₂ . 2 is the excitation power supply,
A low frequency excitation current I is supplied to an excitation coil L.
3 and 4 are a pair of buffer amplifiers, and their inputs receive the voltages e ₁ and e ₂ generated at the pair of electrodes G ₁ and G ₂ , respectively.
has been added. A differential amplifier 5 amplifies the difference between the outputs e ₃ and e 4 of the buffer amplifiers 3 _{and 4} . 6 is a signal processing circuit, which includes an inverting amplifier 61 that inverts the output e ₅ of the differential amplifier 5, and alternately switches between the differential amplifier output e ₅ and the inverting amplifier output e ₆ in synchronization with the on/off of the excitation current I. a switch 62, a sampling switch 63 that samples the voltage selected by the switch 62 for a certain period of time, an integrator 64 that integrates the sampled voltage, and an output e ₇ of the integrator 64.
An AD converter 65 that converts the
It has a microprocessor 66 that performs desired digital calculations based on the digital signal from the AD converter 65, and a DA converter 67 that converts the output of the microprocessor 66 into an analog signal. 7 is a non-full water detection circuit which includes a sampling switch 71 that samples the output _e3 of the buffer amplifier 3 for a certain period of time, an integrator 72 that integrates the sampled voltage, and a sampling switch 73 that outputs the output _e8 of the component amplifier 72. sample hold circuit 74 and sample hold circuit 7
A comparator 7 that monitors the output e ₉ of 4 and outputs a non-full water detection signal AL when e ₉ exceeds the set voltage e _t .
It consists of 5. Note that the synchronous pulse Po to the excitation power source 2 and the pulse that drives the changeover switch 62
P ₁ , the pulse P ₂ that drives the sampling switch 63, and the reset switch SW ₁ of the integrator 64.
The microprocessor 66 generates _a pulse _P3 that drives the sampling switch 71, a pulse _P4 that drives the reset switch _SW2 of the integrator 72, and a pulse _P6 that drives the sampling switch 73. Indicates when to do so.

The operation of the electromagnetic flowmeter of the present invention constructed as described above will be explained below with reference to the waveform diagrams of FIGS. 2 and 3. FIG. 2 is a waveform diagram when the water is full, and FIG. 3 is a waveform diagram when the water is not full. In both figures, A, B, C, D, H, H, G are pulses Po, P ₁ , P ₂ , generated by the microprocessor 66.
In the waveforms of P ₃ , P ₄ , P ₅ , and P ₆ , H is the waveform of the excitation current I, R is the waveform of the signal component e _s of the detection voltage, and N is the waveform of the noise component e _o of the detection voltage. First, we will explain the operation when the water is full. The excitation power source 2 is the pulse Po from the microprocessor 66 (see Figure 2 A).
In synchronization with , a low-frequency excitation current I as shown in FIG. In the electromagnetic flowmeter transmitter 1, when an excitation current I is supplied to an excitation coil L, detection voltages e ₁ and e ₂ are generated at electrodes G ₁ and G ₂ . Conduit P is connected to detection voltages e ₁ and e ₂
In addition to _the signal _component e _s as _shown in FIG _. Noise components as shown in Figure 2 are generated due to
e _o is also weighted. At detection voltages e ₁ and e ₂ , the signal components e _s are generated in opposite phases to each other, but
The noise component e _o is generated in the same phase. These detection voltages e ₁ and e ₂ are applied to the differential amplifier 5 via buffer amplifiers 3 and 4, respectively, so that the noise component e _o is removed and the signal component e _s is effectively extracted. Moreover, the output e ₅ of the differential amplifier 5 and the voltage e ₆ obtained by inverting e ₅ by the inverting amplifier 61 are synchronized with the excitation current I, and the switch 62 is driven by a pulse P ₁ as shown in FIG.
After being alternately selected, the switch 63 driven by the pulse _P2 generated at the timing shown in _FIG . Noise components e _o that have passed through the differential amplifier 5 due to unbalanced configuration or the like are also effectively removed. Also, in the integrator 64
The time t _s for integrating e ₅ and e ₆ is determined by the pulse P ₂ from the microprocessor 66 so that it is equal to the commercial power supply period (for example, 20 ms in the 50 Hz band) or an integral multiple thereof in order to remove power frequency noise. The ON time of the switch 63 is controlled. The output e ₇ of the integrator 64 is converted into a digital signal by an AD converter 65 and provided to a microprocessor 66 . The microprocessor 66 performs digital calculations based on the digital signal from the AD converter 65, calculates the flow rate of the fluid, and sends the calculation results to the DA.
to the converter 67 and the output terminal 68 of the signal processing circuit 6
outputs an output voltage e ₀ related to the fluid flow rate.

Next, in a non-full state where the degree of fluid filling in the pipeline is below the allowable value, the electrodes G ₁ and G ₂ are out of contact with the conductive fluid, and the electrode impedance becomes extremely large, as shown in Figure 3. The signal component e _s becomes zero, but the power supply voltage from the excitation power supply 2 remains unchanged at the electrode.
In addition to G ₁ and G ₂ , a noise component e _o having a waveform as shown in FIG. 3 is generated. This noise component e _o is several volts
Depending on the degree, the maximum amplitude of the signal component e _s in the full water condition
This is a very large value compared to 10mV. Therefore, if the output _e3 of the buffer amplifier 3 is fed to the integrator 72 via the sampling switch 71 driven by the pulse _P4 synchronized with the pulse Po (excitation current I), the output _e8 of the integrator 72 will be filled with water. It varies greatly depending on the state and non-full water state. Therefore, the sample hold circuit 74 obtained by driving the sampling switch 73 using the output _e8 of the integrator 72 with the pulse _P6 shown in FIG.
The set voltage of comparator 75 that monitors the output _e9 of
By appropriately selecting e _t , the output of the comparator 75 is inverted when the water is not full, and the non-full water detection signal AL is generated.

In the above description, the output e3 of the buffer amplifier 3 is synchronously rectified and taken out using the sampling switch 71 and the integrator 72 as the non-full water detection circuit 7, but the output _e3 of the buffer amplifier 3 can also be taken out using other synchronous rectification circuits. good. In addition, in the above description, the buffer amplifier 3
Although the case where the non-full water detection signal AL is obtained by monitoring the output e ₃ of the buffer amplifier 4 has been exemplified, the non-full water detection signal AL may be obtained by monitoring the output e ₄ of the buffer amplifier ₄ . The non-full water detection signal AL may be obtained by monitoring the detection voltages e ₁ and e ₂ of G ₂ .
Further, in the above description, the signal processing circuit 6 is exemplified as one that performs digital calculations using the microprocessor 63, but circuits with various circuit configurations such as a circuit that performs analog calculations can be used as necessary.

As explained above in detail, in the present invention, in order to detect whether or not the electromagnetic flow transmitter is filled with the fluid to be measured, some kind of disturbance, such as current, is applied to the detection electrode. without flowing,
We focused on the nature of the voltage output from the detection electrode, that is, the voltage generated when the electromagnetic flowmeter transmitter is not full of water is much larger than the voltage generated when the fluid to be measured is full of water inside the electromagnetic flowmeter transmitter. Since this difference in size is detected by comparing the set voltage set in advance based on experience and the voltage related to the detection voltage, it does not have any negative effect on normal flow rate measurement. It is possible to easily detect a non-full water condition without any need for water.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing one embodiment of the electromagnetic flowmeter of the present invention, and FIGS. 2 and 3 are waveform diagrams for explaining its operation. 1... Electromagnetic flow meter transmitter, 2... Excitation power supply,
3, 4... Buffer amplifier, 5... Differential amplifier,
6... Signal processing circuit, 7... Non-full water detection circuit.

Claims (1)

[Scope of utility model registration request] an electromagnetic flowmeter transmitter through which a fluid to be measured flows; an excitation power source that switches at a predetermined switching timing to supply a low-frequency excitation current to the excitation coil of the electromagnetic flowmeter transmitter; and a pair of electromagnetic flowmeter transmitters. a differential amplifier to which detection voltages generated at the respective electrodes are applied via a buffer amplifier; a signal processing circuit to which the output of the differential amplifier is input and which executes a flow rate calculation using the same and outputs it as a flow rate signal; sampling means for sampling a voltage related to the voltage in synchronization with the switching timing; synchronous rectification means for synchronously rectifying the sample voltage sampled by the sampling means; and holding the output of the synchronous rectification means as a hold voltage. and a voltage level at a detection point of a voltage related to a detection voltage generated in the electromagnetic flowmeter transmitter when the inside of the electromagnetic flowmeter transmitter is filled with the fluid to be measured. a setting means set to a sufficiently large set voltage;
An electromagnetic flowmeter characterized in that a comparison means is provided which compares the hold voltage and the set voltage and outputs a non-full water detection signal when the hold voltage exceeds the set voltage.